1. Field of the Invention
The present invention relates to a nonaqueous electrolyte battery, a lithium-titanium composite oxide, a battery pack and a vehicle.
2. Description of the Related Art
A vigorous research is being conducted on a nonaqueous electrolyte battery having a high energy density in which lithium ions are migrated between the negative electrode and the positive electrode for charging and discharging the battery.
Various properties are required for the nonaqueous electrolyte battery depending on the use of the battery. For example, the discharge under a current of about 3C is expected when the nonaqueous electrolyte battery is used in a digital camera, and the discharge under a current of at least about 10C is expected when the nonaqueous electrolyte battery is used in a vehicle such as a hybrid electric automobile. Such being the situation, the large current characteristics are particularly required in the nonaqueous electrolyte battery used in the technical fields exemplified above.
Nowadays, a nonaqueous electrolyte battery in which a lithium-transition metal composite oxide is used as a positive electrode active material and a carbonaceous material is used as a negative electrode active material has been put to the practical use. In general, Co, Mn or Ni is used as the transition metal included in the lithium-transition metal composite oxide.
In recent years, a nonaqueous electrolyte battery in which a lithium-titanium composite oxide having a high Li absorption-release potential relative to the carbonaceous material has been put to the practical use. Since the lithium-titanium composite oxide is small in the change of volume accompanying the charge-discharge of the battery, the lithium-titanium composite oxide is expected to improve the charge-discharge cycle characteristics of the secondary battery.
Among the lithium-titanium composite oxides, the Spinel type lithium titanate is expected to be particularly useful. The Spinel type lithium titanate can be synthesized by, for example, mixing lithium hydroxide with titanium dioxide, followed by baking the resultant mixture. If the baking is insufficient in this synthesizing process, obtained are lithium-titanium composite oxides containing an anatase type TiO2, a rutile type TiO2, and Li2TiO3 as impurity phases in addition to the Spinel type lithium titanate.
It is disclosed in Japanese Patent Disclosure (Kokai) No. 2001-240498 that lithium-titanium composite oxides containing the Spinel type lithium titanate as a main component, having a small amount of the impurity phases noted above, and also having a crystallite diameter of 700 to 800 Å can be used as the negative electrode active material having a large capacity.